Protesters have rallied together outside an aquarium to demand it releases 15 penguins from their “concrete prison” without fresh air and daylight.

A dozen activists descended on Sea Life London Aquarium (SLLA) to call for the animals to be moved from the basement enclosure.

The Express understands the penguin habitat is being revamped and is set to re-open next month.

Dominic Dyer, of the Born Free Foundation, said: “There are hundreds of tourists who are coming here hour by hour to visit this facility from Britain and around the world.

“We’re here because we’re drawing to their attention to what we believe is one of the worst cases of exploitation and cruelty of penguins that you’ll see anywhere in the world.”

Speaking through a megaphone, he slammed the enclosure, claiming it to be a “concrete prison”.

Dominic added: “There is no justification for keeping penguins in a concrete basement prison of this facility or any other facility in Britain or around the world.”

One visitor headed for the tourist attraction in Central London told protesters how she demanded a refund on her ticket after finding out about the plight of the penguins.

Several others signed the group’s petition which has amassed nearly 5,000 signatures so far.

More than 20 MPs, over a dozen animal welfare groups and celebrities like Chris Packham and Feargal Sharkey have backed calls for the animals to be moved to a more suitable environment.

Freedom for Animals’ Isobel McNally urged people to sign the groups’ petition – backed by the Express – and to contact their MPs to sign a Parliamentary Early Day Motion on the issue.

She said: “We’re campaigning to have the penguins removed and rehomed to a more suitable environment which Sea Life has more than enough money to fund.”

Campaigners praised the Express’s crusade to free the penguins after the paper was threatened with legal action for daring to call the animals “captive”.

Protester Madeleine O’Halloran said: “These penguins are trapped inside of Sea Life. This is not conservation. They are not endangered or even threatened in the wild. They are being held here purely for entertainment.”

Josephine Wilson, who started protesting outside the facility two years ago, told how the support for the Express, Born Free and Freedom for Animals means there will be increasing pressure on the aquarium to move the animals.

A SLLA spokeswoman said: “The welfare of all the animals in our care is of paramount importance to us at Sea Life and we are committed to delivering the highest levels of care through our team of dedicated welfare experts, both internal and external.

“Sea Life conforms to all requirements under the Standards of Modern Zoo Practice by providing the relevant zoo licensing authorities with access to its animal records.

“This is in addition to regular visits including zoo licence inspections by these local authorities, alongside additional external inspectors and independent vets, who monitor animal welfare and data on an ongoing basis and will continue to do so.

“SLLA also carries out its own regular health checks on all the animals in its care, while an independent specialist vet also visits every two months for routine assessments, and can also be contacted daily with any other concerns.

“The Gentoo penguin habitat at SLLA was designed with help and advice from specialist vets. It provides an excellent balance of water and land for the penguins which enables them to express their normal behaviours and there is space for them to ensure they have sufficient privacy.

“As part of its overall mission, SLLA provides an opportunity to share the wonders of the natural world in an accessible manner. With the opportunity to educate more than a million people who visit SLLA from all around the globe each year to care for the world’s oceans and the marine life within it, we believe this is a hugely positive thing.”

To sign the petition to free the penguins, visit the page here.